Fading elimination in radio picture-transmission systems



May 6, 1930.

FADING ELIMINATION IN RADIO PICTURE TRANSMISSION SYSTEMS Filed June 19. 1928 mvzmog F TZ SCHROTEK BY g fZg d/W ORNEY Patented ay 6, 1930 FF I C E FRITZ SCHRGTER, 0F BERLIN, GERMANY, ASSIGNOB TO TELEFUNKEN GESELLSCHAIiT FNR DRAHTLOSE TELEGRAPHIE M. B. H., 0F BERLIN, GERMANY, A CORPORATION OF GERMANY FADING ELIMINATION IN RADIO PICTURE-TRANSMISSION SYSTEMS Application filed June 19, 1928, Serial No. 286,617, and in Germany May 21, 19%.

it has beenfound in picture transmission work that dark stripes or streaks are produced in the incoming picture due to extinction or fading of the incoming signal energy. The dark stripes exercise a disturbing effect in the total impression of thepicture when ever they are of appreciable width, in other words, the diminution of the incoming strength of radio frequency oscillations has a disturbing effect in the transmitted picture whenever the duration of time during which the decrease in incoming intensity occurs is so great that it covers several lines in the picture along which the picture is scanned or explored at the sending end, or reassembled at the receiving end. In picture transmission apparatus of the kindrece'ntly used, the width of a picture exploring line amounts to about 0.2 mm. If a single line'is skipped, this will result in no appreciable effect in the transmitted picture. However, as a general rule, the diminution or fading of the electromagnetic waves continue for an appreciably longer time than for a single line so that in the usual exploring or reassembling methods in which the constituent or vertical picture lines are successively transmitted, the disturbance will manifest itself in several adjacent lines.

'lhe present invention .discloses a transmission method in which these disturbances due to fading and diminution of the incoming current strength are eliminated. For this purpose, according to the present invention,

I transmission of the picture is effected in such a way that exploration of the picture at the sending end and consequently the reassemloling thereof at the receiving end, is not effected by the form of closely adjacent and successive lines, but the transmission and reception is accomplished in such a way that first a few lines being at a relatively great distance from each other in the picture are consecutively transmitted, and by'that next a few lines an equal distance apart are transmitted, but so that the relative position of the picture and the exploring element is shifted a distance equal to thewidth of an exploring line compared with the preceding position. Hence, after this second exploration, pairs of adjacent lines] being a relatively great distance apart are transmitted. During the third exploration of the picture, the position between picture and exploring means is again shifted so that in each case three lines come to be placed contiguous to one another, and so on, until the whole picture has been explored.

This process may be explained in a schematic manner. Suppose B is the picture to be explored and reassembled. Then, in the first stage of transmission or exploration, lines 1, 2, 3, are consecutively transmitted, during the second stage the lines 4, 5, 6; in the third stage the lines 7, 8, 9, etc. It will be readily understood that by such a sequence or order in transmission, lines located adjacent in space are in dissimilar time sequence. Thus, any

ossible occurring extinctlon or fading in the incoming current having the duration in transmission of three lines, and which in the customary transmission method would thus result in a dark stripe equalling the width of three lines, in the new transmission method here disclosed would result in an equal number of stripes being more or less separated in space, for instance, stripes 1, 2, 3, in the diagram, and since the width of such a dark stripe is, comparatively speakin ver small, it will beseen that the ensuing distur ing effect will become inappreciable.

The disposition of the different means to practice this transmission method as here disclosed follows from the basic principle of the process. As regards the detail means to be employed, it will be noted that these, of course, may he of widely different nature, and the attendant problemsare easily solvable hy means and methods known at the present state of the art of exploring and reassembling the picture, and the art of synchronization. For instance,-the exploring means may be of a kind so that several perforation lines are provided which explore the picture consecutively at relatively great distances, and that next, after the first exploring stage of the picture, the picture strip 1s shifted by convenient drive means by the width of an exploring line. In conform ty therewith, of course, also the reassemblmg means at the receiving end should be conreproduced picture lines both as to space and time, must be worked or effected in the same manner so as to suit the operation of the device at the sending end.

It will be understood that the present process is not confined to the' case hereinbefore discussed in more detail in which ex- .ploration and reassembly is effected by or along lines parallel to one another. Indeed, according to the spirit of the invention every and any method is applicable in which ar-. .rangements have been so made that spatlal separation of explored and reassembled picture elements contiguous as to time is effected, and that, inversely, picture elements close together as to space or location and tobe transmitted are actually transmitted, i. e., explored and reassembled or recorded at more or less great intervals of time.

- vThe broad idea of analyzing and reproducing an image with consecutive lines of scanning or exploration and reproducing or re,- assembling widely separated is broadly shown by British patent to Stephenson et al., 218,766v The transmission, however, which is illustrated by this British patent is confined to television and the idea expressed is that of lowering the exploring speed without impairing the fineness or delicacy of the decomposition of the picture. For this purpose in the British patent a sequence or series of lines is first traced over the'picture to be explored, that is, a row of parallel lines being a multiple distance of the line width away from each other and upon the recurrence or return of the luminous spot or focus the interlines are filled up in accordance with the diagram shown by Fig: 13 of the British patent.

In a scheme of the character disclosed by the British patent the idea is merely that of television and the picture must be transmitted at least ten times a second to make any result such that the persistency of vision enables' one to visualize the movement of the object being transmitted.' However, this mission of an adjacent line is made comparatively large, or, in'other words, of a time duration considerably greater than the time period during which the persistency of vision would enable an observer to view a picture or, to express it in still other terms, the time period between successive lines is great compared with the mean fading period. It is thus possibleor probable that the exploring focus will not record all of the adjacent lines inside the fading period. The ensuing photographic picture, therefore, will exhibit diminished blackening during the fading periods so far as the ensemble effect is concerned', but eveninview of the diminished blackening the facsimile will be adequately clear throughout anda clear cut "result will be obtained.

Having now described my invention,- 1 claim: a

The method of transmitting and receiving pictures by radio which includes exploring and reassembling a picture along a number of lines separated one'from the other a dis-, tance amounting to several times the width of a single exploring line, exploring and reassembling the picture along lines adjacent said first named set of lines at widely interrupted time intervals from said first exploration and reassembling, and continuing the exploring and reassembling of adjacent lines until the entire space between the first named separated lines of exploration and reassemblage has been explored and reassembled by separating each successive adjacent exploration and reassemblage by time FRITZ SCI-IRGTER.

scheme does not take into account the fact reception of signals that the fading period would usually and, in fact, practically a1- ways does, last for more than one-tenth of a second and if the means disclosed in the above identified British patent were used for photographi'c'facsimile transmission and reception no useful registration or recording of a picture would ensue.

Itis, therefore, a basic idea of my inventionto utilize a resolution of the picture exploration for the purpose of producing a legible facsimile copy which method diifers from the scheme disclosed by the British patent in that the time interval between the transmission of a definite line and the trans- 

